JP2001118660A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug of which material of precious metal ignition part is excellent in heat resistance and oxidation and attrition resistance and yet has a good workability and that does not easily suffer from abnormal corrosion even when it is applied to leaded gasoline engine. SOLUTION: With this spark plug 100, the ignition parts 31, 32 are composed mainly of Rh as the principal component, and Rh series precios metal alloy including either one kind or more than two kinds of additional metal element components chosen from Re, Ru, Ir, W, Mo, and Os within 3 to 38% mass.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug used for an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, the above-described spark plugs are of a type in which a noble metal tip mainly composed of Pt, Ir, or the like is welded to the tip of an electrode in order to improve spark wear resistance. Many have been proposed.

However, in recent years, the temperature in the combustion chamber has tended to increase due to the high performance of the internal combustion engine, and in order to improve the ignitability, many types of engines have a spark plug ignition portion protruding into the combustion chamber. Is being used. In recent years, as part of maintenance-free measures for automobile engines, severe demands that cannot be imagined from the previous situation, such as continuous running of 160,000 km or more without replacement of spark plugs, have been issued. ing.

[0004]

In the above-mentioned situation, various problems are unavoidable no matter how the noble metal tip is used. For example, in the case of a Pt-based noble metal tip, the heat resistance may be slightly insufficient depending on the use condition of the internal combustion engine. For example, if the spark generation position in the ignition part is biased and the tip temperature rises locally, The chip is partially melted (hereinafter, referred to as a sweating phenomenon), for example, the surface of the chip becomes uneven, and the gap of the spark discharge gap is locally narrowed, which may cause a problem such as gap short circuit. On the other hand, when an Ir-based noble metal tip having a higher melting point than Pt is used, the heat resistance is greatly improved, but since Ir has a property of being easily oxidized and volatilized at a high temperature, long-time high-speed running is possible. When the temperature rises above a certain temperature, the ignition portion is rapidly consumed and the spark gap interval is increased. Another problem is that Ir is poor in ductility or malleability at both room temperature and high temperature. Therefore, it is necessary to manufacture a chip for forming a ignited portion by processing such as forging, rolling or punching. In addition, there is a disadvantage that the material yield and the production efficiency are reduced and mass productivity is deteriorated.

As another problem, leaded gasoline to which tetramethyl lead or the like is added as an anti-knock agent is still used in some countries and regions where lead-free fuel of gasoline engines is delayed. . In these countries and regions, spark plugs using noble metal chips have begun to be used in high-end vehicles and the like. However, according to studies by the present inventors, Pt is not used for engines using leaded gasoline.
When a spark plug using an ignition system based on Ir or Ir is applied, the ignition system is abnormally corroded due to the effect of the Pb (lead) component contained in gasoline, and only a durability far from the originally expected level can be obtained. It turned out to be gone.

An object of the present invention is to provide a spark plug having a noble metal ignition portion, wherein the ignition portion is made of a material which is excellent in both heat resistance and oxidation wear resistance and has good workability. Also, an object of the present invention is to provide a spark plug which is less likely to cause abnormal corrosion of a noble metal firing portion even when applied to a leaded gasoline engine, and which can secure the excellent durability inherent in the noble metal firing portion.

[0007]

A spark plug according to a first aspect of the present invention has a center electrode, an insulator provided outside the center electrode, and a spark plug provided outside the insulator. A metal shell, a ground electrode disposed so as to face the center electrode, and a firing portion fixed to at least one of the center electrode and the ground electrode to form a spark discharge gap. As a main component, and as additional metal element components, Re, Ru, Ir, W, and Mo.
And an Os-based precious metal alloy containing one or more selected from Os in the range of 3 to 38% by mass.

The ignition portion can be formed by welding a tip mainly composed of the Rh-based noble metal alloy to a ground electrode and / or a center electrode by welding. In this case, the term "ignited portion" as used herein means a portion of the joined chips that is not affected by the composition change due to welding (for example, a portion alloyed with the material of the ground electrode or the center electrode by welding). (The remaining part excluding).

In the spark plug according to the present invention,
Rh is used as a main metal element component of the Rh-based noble metal alloy constituting the ignition portion, and one or more selected from Re, Ru, Ir, W, Mo, and Os as additional metal element components. In a range of 3 to 38% by mass. Since the melting point of Rh is about 1960 ° C., which is higher than at least 1769 ° C. of Pt, it has better heat resistance than the conventional Pt-based ignition part. On the other hand, Rh
Has a lower melting point than Ir but a higher melting point than Rh.
(Melting point: about 3180 ° C), Ru (melting point: about 2250)
° C), Ir (melting point: about 2443 ° C), W (melting point: about 33
80 ° C), Mo (melting point: about 2630 ° C) or Os
Since the added metal element component (melting point: about 3045 ° C.) is blended in the above composition range, the heat resistance is greatly improved.

As a result, it is possible to prevent or suppress the sweating phenomenon which is a problem in the ignition portion of the Pt-based noble metal alloy, as well as to realize a heat resistance comparable to that of the conventional Ir-based ignition portion. Is done. Also, unlike Ir-based noble metal alloys, Rh-based noble metal alloys have good resistance to oxidation and wear at high temperatures, so that their durability is remarkably improved even in an environment where the temperature of the ignition part is significantly increased. Further, the Rh-based noble metal alloy having the above composition constituting the ignition portion has much better workability than the Ir-based noble metal alloy, for example, has relatively low hardness, large deformability, and excellent ductility. By taking advantage of this fact, the noble metal tip for forming the ignition portion can be manufactured extremely efficiently and with a high yield, which greatly contributes to a reduction in manufacturing cost.

[0011] Further, the ignition portion is made of Rh mainly composed of Rh.
The spark plug of the present invention mainly composed of a precious metal alloy, when applied to an engine using leaded gasoline, effectively prevents corrosion derived from the lead component in gasoline (hereinafter referred to as lead corrosion). Can be suppressed. Thus, according to the present invention, a Pt-based noble metal alloy or Ir
Disclosed is a spark plug having an epoch-making performance in which all the drawbacks of the ignition portion due to the precious metal alloy are solved.

If the amount of the added metal element component exceeds 38% by mass, it is not possible to sufficiently secure lead corrosion resistance when applied to a leaded gasoline engine. Further, depending on the type of the added metal element component, the oxidation resistance of the ignition portion may be impaired. In addition, in order to maintain good workability of the alloy, it is desirable that the amount of the added metal element component is limited to 35% by mass or less. For example, when the workability of the material does not matter so much as in the case of manufacturing chips by a sintering method, the compounding amount of the additional metal element component is set to 38.
It is also possible to further increase the heat resistance of the ignition part by increasing it to about mass%. On the other hand, when a chip is manufactured by hot working of a molten ingot, it is desirable to keep the amount of the added metal element component at 35% by mass or less so as not to lower the manufacturing efficiency or the yield due to the deterioration of workability. .

It should be noted that which of the following problems occurs, that is, the deterioration of the oxidation resistance and the deterioration of the workability, also depends on the type of the added metal element component. For example, if the compounding amount of Ir, which is easily oxidized and volatilized at a high temperature, becomes too large, it is natural that the oxidation resistance of the ignition portion is deteriorated. In addition, excessive mixing of Ru, which easily forms volatile oxides, causes similar problems. Although not as remarkable as Ir and Ru, Re and W may also lead to a decrease in the oxidation and wear resistance of the ignited portion when blended beyond the above composition range. On the other hand, if Re, Ru or Ir is excessively blended, the ductility of the material at high or low temperature is impaired, and workability is likely to be reduced. The amount of the added metal element component is more preferably adjusted in the range of 5 to 15% by mass. For example, with respect to metal element components such as Ir and Ru, which easily generate highly volatile oxides at high temperatures (for example, 900 ° C. or higher), the content of the metal element components is set to 15% by mass or less, so that the acid resistance of the ignition portion is reduced. It is possible to further ensure the chemical consumption. Although the volatility of the oxide is not as high as these elements, Re and Mo are also easily mixed at a relatively low temperature (for example, around 600 to 700 ° C.). It can be said that the following is desirable.

On the other hand, if the amount of the added metal element component is less than 3% by mass, the effect of improving the heat resistance by the added metal element component becomes insufficient.

Next, the content of Rh as the main metal element component is desirably 60 to 97% by mass. R
When the content of h is less than 60% by mass, the oxidation-based wear resistance or workability of the Rh-based noble metal alloy constituting the ignition portion becomes insufficient, and the object of the present invention cannot be achieved. On the other hand, when the content of Rh exceeds 97% by mass, the content of the added metal element component for improving the heat resistance is insufficient, and the effect of improving the heat resistance by the addition of the added metal element component is not sufficient. Will be enough. On the other hand, from the viewpoint of better securing the lead corrosion resistance, the content of Rh is desirably adjusted to a slightly higher range than the above, in the range of 62 to 97% by mass.

When attention is paid to individual elements, a more desirable compounding range for Rh may exist individually depending on what property is given priority. For example, from the viewpoint of ensuring good workability, impact resistance, or durability of the ignited portion, each element is not less than 3% by mass and not more than the solid solubility limit with respect to Rh (the solid solubility limit varies depending on the temperature. However, it can be said that it is desirable to mix them within the range of (value at room temperature as a guide). When the element is blended beyond the solid solubility limit, a material structure in which a plurality of phases are mixed is exhibited, and for example, workability and impact resistance may be impaired due to an increase in deformation resistance and a decrease in ductility. For example, when a structure in which a phase mainly composed of Rh (hereinafter, referred to as a main component phase) and a phase mainly composed of an additive metal element component (hereinafter, referred to as an additive component phase) is mixed, the main component phase is used. Is generally highly deformable,
Since the additive component phase mainly composed of Ru or Re has a dense hexagonal packing (hcp) structure with low deformability, workability may be reduced. The same can be said for the components (W, Mo) that form an intermediate phase that is hardly deformed with Rh. In addition, although the hcp structure is not shown,
Since r also has a low deformability of the generated additive component system phase, workability may be reduced.

On the other hand, from the viewpoint of improving the heat resistance, it can be said that a component which can be expected to significantly increase the liquidus temperature even with a relatively small amount of compounding is desirable. In this case, although it seems that the additive metal element component having a high melting point is advantageous in improving the heat resistance, a known binary equilibrium diagram of each component with respect to Rh (for example, Binary Alloy Phase Diagrams (Second Edition))
plus Updates version1.0), 1996, ASM Internationala
As far as l) is referred, for example, in the range of the amount of the added metal element component in the present invention, it cannot be said that the higher the melting point of the added metal element component, the greater the effect on the liquidus temperature rise is. is there. For example, among the added metal element components, W having the highest melting point in a simple substance state has an average liquidus temperature rise rate of about 5 ° C. per 1 mass% in the above composition range, but has a slightly lower melting point. Re reaches nearly 30 ° C. The liquidus temperature rise rate can also be considered as an index indicating the magnitude of the effect of improving the heat resistance. In this respect, if the order of the effect of improving the heat resistance of the added metal element component is shown, Re>Os>Ir>W> Ru > Mo.

From the viewpoints of both the solid solubility limit with respect to Rh at room temperature and the effect of improving the heat resistance, the desirable compounding ranges of the respective components are listed as follows.
An overlap with the desirable range of 5 to 15% by mass described above is shown, and a more desirable range is shown). Re: 3 to 20% by mass (5 to 15% by mass). -Ru: 5 to 34.5 mass% (10 to 15 mass%). Ir: 5 to 35% by mass (5 to 15% by mass). -W: 5 to 23 mass% (5 to 15 mass%). -Mo: 5 to 8 mass%. Os: 5 to 35% by mass (5 to 15% by mass).

In order to ensure the lead corrosion resistance, more desirable elements to be added to the Rh-based noble metal are Re, Mo, Ir.
And Ru. In particular, regarding the content of Ir in the Rh-based noble metal, the content is preferably set to 3 to 38% by mass.
It is desirable to achieve both heat resistance and lead corrosion resistance of the ignition part, and more desirably, the Ir content is 13 to 30% by mass.

Next, as an alloy chip for forming the ignition portion, a chip formed by subjecting a molten alloy obtained by mixing and melting a raw material to a predetermined composition to a predetermined processing is used. it can. In addition, "processing" here means
At least one of rolling, forging, cutting, cutting, and punching is meant to be performed alone or in combination. In this case, processing such as rolling, forging, or punching can be performed by so-called hot working (or warm working) performed by raising the temperature of the alloy to a predetermined temperature. The processing temperature depends on the alloy composition.
The temperature is preferably set to 0 ° C. or higher. The chip material in the spark plug of the present invention has particularly good properties for hot stamping, for example, a molten alloy is processed into a plate by hot rolling, and the plate is further subjected to a predetermined process by hot stamping. If a chip is formed by punching into a shape, the chip manufacturing efficiency is significantly improved, and the chip manufacturing cost can be significantly reduced. Note that a method is also possible in which a molten alloy is worked into a linear shape or a rod shape by hot rolling or hot forging, and then cut into a predetermined length in a length direction to form a chip.

In each of the configurations of the present invention described above, in the Rh-based noble metal alloy constituting the ignition portion, when the concentration distribution of the added metal element component has a stripe-like density, the direction of the stripe is changed to, for example, The ignition portion can be formed so as to be substantially parallel to the voltage application direction (that is, the discharge direction) at the ignition portion (hereinafter, referred to as a parallel mode). According to this, the following effects are achieved. When a stripe-like density distribution occurs, directivity of the alloy crystal orientation tends to occur in the direction of the density stripe. For example, regions having a large difference in the concentration of the added metal element component also have a difference in the coefficient of thermal expansion, and when the cooling and heating cycle is repeated on the generated ignition portion, the consumption of the ignition portion proceeds due to separation along the gray stripes. There is. It is also conceivable that peeling may proceed due to local corrosion near the boundary of the gray stripes. However, in any case, as shown in FIG. 2C, this peeling is performed in the voltage application direction, which is the direction of the light and dark stripes (J) in the above-mentioned parallel mode.
That is, since the shape of the spark discharge gap (g) occurs in the direction of the gap, the remaining alloy crystal of the ignition portion (31) can relatively easily maintain the dimension in the direction of the gap. Therefore,
There is an advantage that the interval of the spark discharge gap g is hard to change even if a little wear progresses. If the alloy crystal structure extending in the direction of the light and shade stripes has a fibrous shape instead of a plate-like shape, the progress of peeling is slowed down, which is more advantageous.

In the case of a so-called parallel type spark plug in which the side surface of the ground electrode faces the front end surface of the center electrode,
As shown in FIG. 2C, the direction of the light and shade stripes (J) of the ignition portion (31) coincides with the axial direction of the center electrode (3), and the orientation of the alloy crystal is easily aligned in this direction. As a result, the ignition part (31) has good heat conductivity in the axial direction of the center electrode (3), and contributes to the improvement of the heat removal characteristic of the ignition part. The ignition portion (31) is a rod-shaped alloy in which fibrous crystal grains are grown along with the above-mentioned light and shade stripes in the longitudinal direction (can be easily manufactured by rotary forging or wire drawing).
Can be cut into a circle by electrical discharge machining or the like, so that chips can be manufactured. For example, waste is less likely to occur during chip manufacturing, and the manufacturing yield can be improved.

On the other hand, the ignition portion may be formed such that the direction of the light and shade stripes is substantially perpendicular to, for example, the direction of voltage application (ie, the discharge direction) at the ignition portion (hereinafter, referred to as the discharge portion).
Orthogonal mode). According to this, the consumption itself of the ignition portion is suppressed, and the effect of suppressing the increase in the spark discharge gap width is further improved. That is, as shown in FIG. 2B, the direction of the light and dark stripes (J) intersects with the direction in which the discharge voltage is applied, so that the boundary of the light and dark stripes is hardly exposed on the ignition surface (31s). As a result, it is presumed that peeling due to local corrosion near the boundary of the light and shade stripes is suppressed, and that the ignited portion is less likely to be consumed.

In the present invention, in the striped concentration distribution of the additive metal element component, a region where the additive metal element component concentration is equal to or higher than the alloy average value is referred to as an additive metal element system phase region. The smaller area is called the main component phase area. In this case, the Rh-based noble metal alloy has, for example, a main component phase region mainly containing the main component element and a content of the additional metal element component larger than that of the main component phase region,
In addition, the added metal element-based phase region in which the content of the main component element is 97% or less of the main component-based phase region has a flat shape, and is substantially perpendicular to the voltage application direction in the ignition portion, or It can be configured as having a multi-layered structure so as to be substantially parallel.

Here, the individual main component-based phase regions and the individual added metal element-based phase regions in the alloy do not necessarily have to be related to the crystal grain morphology constituting the alloy. At least a part thereof may be a flat aggregated grain region formed by assembling a large number of crystal grains, and the aggregated grain region may be stacked on each other.

The spark plug according to the present invention can be specifically configured as follows. (A) While connecting one end of the ground electrode to the metal shell,
The other end is bent back to the center electrode side, and the side face is arranged so as to face the tip end face of the center electrode. The ignition portion is formed on at least one of the tip surface of the center electrode and the side surface of the ground electrode facing the tip surface, and the main component-based phase region and the additive metal element-based phase region having a flat shape are orthogonal to each other. In the case of (1), the structure has a structure laminated in the axial direction of the center electrode, and in the case of the parallel mode, the structure has a structure laminated in a direction substantially orthogonal to this.

(B) The firing part is fixed to the front end face of the center electrode. The ground electrode has one end connected to the metal shell and the other end bent back toward the center electrode, and is disposed such that the front end surface thereof faces the side surface of the firing portion. The ignition portion has a structure in which the main component-based phase region and the additive metal element-based phase region each having a flat shape are stacked in the axial direction of the center electrode in the case of the orthogonal mode, and in the case of the parallel mode. Has a structure laminated in a direction substantially perpendicular to this.

In this specification, the term "flat shape" means that the maximum dimension in the laminating direction is smaller than the maximum value of the dimension in any direction perpendicular to the laminating direction.
For example, the main component phase region and the additive metal element phase region are:
Each of them may be formed in a plate shape, or may be formed in a rod shape or a fibrous shape which is stretched in one direction. In addition, as a matter of course, in the present invention, the morphology of the ignition portion is not limited to the above, and, for example, the above-mentioned striped component shading does not necessarily have to be clearly generated.

The materials constituting the chip include Group 3A (so-called rare earth element) and Group 4A (T
An oxide (including a composite oxide) of a metal element belonging to i, Zr, Hf) can be contained in the range of 0.1 to 15% by mass. As a result, consumption of the added metal element component, particularly Ir, Ru, Re, and W due to oxidation and volatilization, is more effectively suppressed. If the content of the oxide is less than 0.1% by mass, the effect of preventing the oxidation and volatilization of the added metal element component by the addition of the oxide cannot be sufficiently obtained. On the other hand, when the oxide content exceeds 15% by mass, the heat resistance of the chip may be impaired. In addition, as the above-mentioned oxide, Y ₂ O ₃ is preferably used, but in addition, La ₂ O ₃ , ThO ₂ , ZrO _{2 and the} like can be preferably used.

The spark plug of the present invention can be configured as a so-called parallel facing type spark plug in which the ground electrode is disposed so that the side surface faces the tip surface of the center electrode. In such parallel-facing spark plugs, the problem of lead corrosion when used in a leaded gasoline engine is more likely to occur on the ground electrode side where the electrode temperature tends to rise, and in extreme cases, the ignition portion on the ground electrode side It is possible that only one is significantly affected by lead corrosion. In this case, the ground electrode side ignition portion fixed to the ground electrode side is Rh.
It is desirable to mainly use a precious metal alloy.

On the other hand, in the above-mentioned parallel opposed type spark plug, a configuration in which the center electrode firing portion is fixed to the front end surface of the center electrode can be adopted. When the center electrode-side ignition portion is not significantly affected by lead corrosion, the ignition portion can be mainly composed of an Ir-based noble metal alloy having Ir as a main component and having excellent heat resistance.

Further, the spark plug according to the second invention is
A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, a ground electrode disposed so that a side surface faces a tip end surface of the center electrode, and a ground. A ground electrode-side ignition portion mainly composed of a Rh-based noble metal mainly composed of Rh and fixed to the side surface of the electrode, and an Ir-based noble metal fixed mainly to the tip end surface of the center electrode and mainly composed of Ir. And a spark discharge gap formed between the ground electrode-side firing portion and the center electrode-side firing portion.

The ignition portion on the ground electrode side, which is susceptible to lead corrosion, is mainly composed of a Rh-based noble metal alloy having excellent lead corrosion resistance, while the ignition portion on the center electrode side, which is less susceptible to lead corrosion, has heat resistance. By mainly using an Ir-based noble metal alloy having a high value, it is possible to achieve both higher levels of the lead corrosion resistance and the heat resistance of the ignition portion. In particular, when using a spark plug with a negative polarity on the center electrode side, the center electrode side ignition portion that is apt to cause spark wear is constituted by an Ir-based noble metal alloy having more excellent spark wear resistance. It is possible to further extend the life of the ignition part. Also,
Although the temperature rise of the ground electrode-side ignition portion is large, the polarity is positive, so that the spark consumption is suppressed as compared with the center electrode side where the polarity is negative. As a result, the Rh-based noble metal constituting the ground electrode-side ignition portion has the content of the above-mentioned additional metal element component for the purpose of improving heat resistance of 3% by mass or less, or the Rh content of 97% by mass or more. (For example, it is possible to constitute only Rh without unavoidable impurities). In the latter case, it can be said that the higher the Rh content, the more advantageous the improvement in lead corrosion resistance.

As the Ir-based noble metal alloy constituting the center electrode side firing portion, for example, the following can be used, but the present invention is not limited thereto. (1) An alloy mainly containing Ir and containing Rh in a range of 1 to 50% by weight (but not including 50% by weight) is used. By using the alloy, consumption of the ignition part due to oxidation and volatilization of the Ir component at a high temperature is more effectively suppressed, and as a result, a spark plug having more excellent durability is realized.

When the content of Rh in the above alloy is less than 1% by weight, the effect of suppressing the oxidation and volatilization of Ir by adding Rh becomes not significant. On the other hand, when the Rh content is 50% by weight or more, the melting point of the alloy decreases, and the effect of improving the heat resistance specific to the Ir alloy becomes insufficient.

Here, as the content of Rh in the alloy increases within the above range, the effect of suppressing the oxidation and volatilization of the ignition part is enhanced. From this viewpoint, the effect of suppressing oxidation and volatilization is most remarkable when the Rh content is 7 to 30% by weight,
More preferably 15-25% by weight, most preferably 18%
~ 22% by weight. However, in the present invention, the reduction of the carbon content in the Ir-based metal constituting the ignition portion to the above-mentioned level has a large effect of suppressing oxidation consumption, so that even if the Rh content is relatively small,
Oxidation and volatilization effects comparable to or higher than those of the conventional spark plug in which the ignition portion is made of an Ir-based metal are achieved. As a result, it is possible to realize a spark plug that is excellent in resistance to oxidation and consumption of the ignition portion while reducing the content of expensive Rh. For example, when the content of Ir in the Ir-based metal is 85% by weight or more as described above, R
The content of h is desirably adjusted in the range of 1 to 15% by weight, more desirably 3 to 10% by weight.

(2) An alloy mainly containing Ir and containing Pt in the range of 1 to 50% by weight is used. By using the alloy, consumption of the ignition part due to oxidation and volatilization of the Ir component at a high temperature is more effectively suppressed, and as a result, a spark plug having more excellent durability is realized. If the content of Pt in the alloy is less than 1% by weight, the effect of suppressing the oxidation and volatilization of Ir becomes insufficient, and the ignition portion is easily consumed, so that the durability of the plug is reduced. On the other hand, when the content of Pt is 50% by weight or more, the melting point of the alloy decreases, and the effect of improving the heat resistance specific to the Ir alloy becomes insufficient. For example, when the content of Ir in the Ir-based metal is 85% by weight or more as described above, the content of Pt is preferably in the range of 1 to 15% by weight, and more preferably in the range of 3 to 10% by weight. It is desirable to adjust.

(3) An alloy containing Ir as a main component and 0.5% by weight or more of Nb is used. By using the alloy, the consumption of Ir component due to oxidation and volatilization at high temperature is more effectively suppressed, and a spark plug having more excellent durability is realized. When the content of Nb in the alloy is less than 0.5% by weight, the effect of suppressing the oxidation and volatilization of Ir by adding Nb becomes insignificant. The content of Nb is desirably 1% by weight or more, and more desirably 5% by weight or more.

In this case, more preferably, Nb is changed to Ir.
It is preferable to use an alloy containing the alloy in the range of the solid solubility limit or less. When Nb is contained in excess of the solid solubility limit for Ir, a brittle intermetallic compound such as Ir ₃ Nb is formed,
A problem may occur in the durability and impact resistance of the ignition part.
For example, the solubility limit of Nb in Ir at room temperature is about 6
Since it is% by weight, when Nb is solely contained, it can be said that it is desirable to set the respective contents to be smaller than the above values. However, when the formation amount of the intermetallic compound is less than a certain value and the influence on the durability of the ignition part is small, the content of Nb may be a value slightly exceeding the solid solubility limit. . From the above, for example, Nb
Is contained alone, the content is 7% by weight or less,
Desirably, the content is 6% by weight or less.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. A spark plug 100 as an example of the present invention shown in FIG.
The insulator 2 fitted inside the metal shell 1 so that the tip 21 projects, and the center electrode provided inside the insulator 2 with the center electrode-side firing portion 31 formed at the tip protruding. 3, and one end is connected to the metal shell 1 by welding or the like, and the other end is bent back to the side, and the side surface is arranged so as to face the front end portion (here, the front end surface) of the center electrode 3. Ground electrode 4 and the like. The ground electrode 4 has a ground electrode-side firing portion 32 formed on the center electrode-side firing portion 31.
The gap between the first electrode 1 and the ground electrode side firing portion 32 is a spark discharge gap g.

The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a hole 6 for fitting the center electrode 3 along its own axial direction. . The metal shell 1 is formed of a metal such as low-carbon steel in a cylindrical shape, forms a housing of the spark plug 100, and has a screw on its outer peripheral surface for attaching the plug 100 to an engine block (not shown). The part 7 is formed.

It should be noted that one of the center electrode side firing portion 31 and the ground electrode side firing portion 32 may be omitted. In this case, a spark discharge gap g is formed between the center electrode side firing portion 31 or the ground electrode side firing portion 32 and the ground electrode 4 or the center electrode 3.

The body portions 3a and 4a of the center electrode 3 and the ground electrode 4 are made of a Ni alloy. On the other hand, the center electrode side firing portion 31 and the ground electrode side firing portion 32 contain 62 to 97% by mass of Rh as a main metal element component, and further contain Re, Ru, Ir, W, Mo as an additional metal element component.
And Os, one or more selected from the group consisting mainly of a Rh-based noble metal alloy containing 3-38% by mass, for example, Ir in a range of 13-30% by mass.

As shown in FIG. 2 (a), the main body 3a of the center electrode 3 has a reduced diameter at the tip end and a flat tip end. Disc-shaped chip 3 whose composition is adjusted to obtain
The center electrode side firing portion 31 is formed by laminating 1 ′, forming a welded portion B along the outer edge of the joint surface by laser welding, electron beam welding, resistance welding, or the like and fixing the welded portion B. In addition, the ground electrode side firing portion 32
The tip 32 ′ is aligned with the ground electrode 4 at a position corresponding to the center electrode side firing portion 31, and a welded portion W is similarly formed along the outer edge of the joint surface, and this is fixed.

For example, these chips are formed into a plate by hot rolling a molten alloy obtained by blending and melting each alloy component so as to have an intended composition, and as shown in FIG. A sheet formed by stamping 300 into a predetermined chip shape by hot stamping can be used. FIG.
(B) schematically shows an example in which a center electrode side firing portion 31 and a ground electrode side firing portion 32 (hereinafter, also referred to as firing portions 31 and 32 when both are generically used) are formed using such a tip. It is shown in a typical way. In addition, as shown in FIG. 5, the chip is processed into a linear or rod-shaped material 210 by one or a combination of two or more of hot forging, hot rolling and hot drawing. May be cut to a predetermined length in the length direction. For example, after being processed into a rod by hot forging, the diameter is further reduced by hot rolling with a grooved roll and hot swaging, and finally processed into a wire having a wire diameter of 1 mm or less by hot drawing. can do. FIG. 2C schematically shows an example in which the ignition portions 31 and 32 are formed using such chips.

The operation of the spark plug 100 will be described below. That is, the spark plug 100 is attached to the engine block at the screw portion 7 and used as an ignition source for the air-fuel mixture supplied to the combustion chamber.
Here, the Rh-based noble metal alloy constituting the center electrode side firing portion 31 and the ground electrode side firing portion 32 forming the spark discharge gap g uses Rh as a main metal element component, and further includes an additional metal. Re, R as elemental components
Since one or more selected from u, Ir, W, Mo, and Os are blended in the range of 3 to 38% by mass, heat resistance and oxidation wear resistance are good. Firing part 3
The Rh-based precious metal alloys having the above-mentioned composition constituting 1, 32 are represented by I
Since it has much better workability than r-based noble metal alloys and can produce Rh-based noble metal alloy chips for forming ignition parts with extremely high efficiency and high yield,
It also contributes significantly to reducing manufacturing costs. Further, the Rh-based noble metal alloy has excellent lead corrosion resistance, and the ignition parts 31 and 3
2, in particular, consumption of the ground electrode side ignition portion 32 due to lead corrosion can be extremely effectively suppressed.

Next, as schematically shown in FIG. 3, the ignition portions 31 and 32 can be configured such that the Rh-based noble metal alloy has the following structure. That is, the content of the additional metal element component is larger than that of the main component phase region and the content of the main component element is larger than that of the main component phase region. 97% or less of the additive metal element-based phase region 51 has a flat shape or a fibrous shape, respectively, in the voltage application direction in the center electrode side firing portion 31 (that is, the direction of the axis O of the center electrode 3 in FIG. 1). On the other hand, a multi-layered structure is formed so as to be substantially perpendicular or substantially parallel to this.

For example, when an alloy raw material is blended at an expected ratio and melted to form an alloy ingot, the above-described main component-based phase region 50 and the added metal element-based phase region 51 are formed by phase separation or component segregation. Are often formed. As shown in FIG. 4, this alloy ingot is heated to, for example, about 700 ° C., and is hot-rolled into a sheet material 300.
In 00, a structure in which a large number of main component-based phase regions 50 and additional metal element-based phase regions 51 are stacked in the thickness direction is generated.
Such a plate material 300 is formed by, for example, punching into a disk shape by hot punching, or by cutting out into a disk shape by electric discharge machining, thereby forming the main component phase region 50 in the axial direction.
Chip 15 in which metal and additive metal element phase region 51 are laminated
0 is obtained.

By using such a chip, for example, as schematically shown in FIG.
Has a structure in which a large number of flat main component-based phase regions 50 and additional metal element-based phase regions 51 are stacked in the axial direction of the center electrode 3 (or in the direction in which the discharge voltage is applied). In this configuration, stripe-like shading occurs in the distribution of the added metal element component, and the direction of the shading can be substantially perpendicular to the voltage application direction (that is, the discharge direction) in the ignition portion. Thereby, the consumption of both the ignition portions 31 and 32 can be effectively suppressed, and the increase of the width of the spark discharge gap g can be effectively suppressed.

In FIG. 4, the reason why the layered structure is formed in the sheet material 300 by hot rolling may be as follows. First, since all of the alloy raw materials are precious metals having a very high melting point, it is considered advantageous to adopt a small batch production method by the following method. That is, as shown in FIG. 6A, each raw metal 60 is blended in a refractory container 62 so as to have an intended composition, and an induction heating coil (or a laser beam, a plasma arc beam, or the like) may be used. The raw material mixture is locally melted by a heat source 63 such as the above, and as shown in FIG. 3 (b), the melting region 200a is gradually moved in a predetermined direction to melt the whole. In addition, in order to obtain a homogeneous alloy, it is desirable to repeat the melting in this method a plurality of times.

Here, since the melting region 200a is directionally cooled by the already solidified alloy portion 200b, the additional metal element-based phase region 51 is included in the main component-based phase region 50.
It is considered that when these are formed by precipitation, each of these phases is likely to precipitate preferentially in the cooling direction. As a result, as shown in FIG. 6C, the obtained alloy ingot 200 has the additive metal element-based phase region 51 in the main component-based phase region 50.
Layer (or column) extending long in the direction of movement of heat source 63
It is thought that it will show the organization of.

Then, as shown in FIG. 7, this is hot-rolled one or more times so that the laminating direction of the additive metal element-based phase region 51 and the main component-based phase region 50 becomes the rolling direction (temperature: : About 700 ° C.), the thickness of the ingot 200 is reduced to become the plate material 300. At this time, the additive metal element-based phase region 51 and the main component-based phase region 50 are considered to maintain the original laminated structure in a form in which the thickness is reduced, and as a result, the plate material 300 is as shown in FIG. It is presumed to have a layered structure.

The crystal grains of the alloy ingot 200 are as follows:
In the state before rolling due to the influence of the above-described directional cooling, corresponding to the additive metal element-based phase region 51 and the main component-based phase region 50,
It is also conceivable that the shape is elongated. However, if hot rolling is performed in the above-mentioned temperature range, crystal grains may be refined by so-called dynamic recrystallization. On the other hand, since the hot rolling temperature is much lower than the temperature at which the alloy becomes a single phase in many systems, regardless of the crystal refinement, the added metal element-based phase region 51 and the main component-based phase region are not affected. The layered structure with 50 is likely to be at least partially maintained. As a result, as shown in FIG. 8, at least a part of each of the regions 50 and 51 becomes a flat aggregated grain region formed by assembling a large number of crystal grains 50a to 51a. In some cases, a structure laminated on each other may be formed.

As shown in FIG. 9 (a), in the state of the ingot, the additive metal element-based phase region 51 and the main component-based phase region 50 do not form a layered morphology, for example, a structure relatively close to an equiaxed crystal. However, even in the case of having a layer structure, it may be crushed by hot rolling to form a layered structure as shown in FIG.

Another possible mechanism is that the additional metal element-based phase region 51 precipitates in the main component-based phase region 50 in a laminar form during the hot rolling or the cooling process after the rolling. Can be

On the other hand, as chips constituting the ignition portions 31 and 32, for example, as shown in FIG. 5, a main component-based phase region 50 and an additional metal element-based phase region 51 are rod-shaped extending in one direction, respectively. Or fibrous tip 15
0 may be used. When such a tip is used, for example, as schematically shown in FIG. 2C, the firing portions 31 and 32 are arranged in a direction orthogonal to the axial direction of the center electrode 3 (or the direction of application of the discharge voltage) It has a structure in which a large number of flat or fibrous main component-based phase regions 50 and additional metal element-based phase regions 51 are stacked. Also in this configuration, stripe-like shading occurs in the distribution of the added metal element component, and the direction of the shading is substantially parallel to the voltage application direction (ie, the discharge direction) in the ignition portion.
In this embodiment, for example, the effect of easily maintaining the interval of the spark discharge gap g at the time of occurrence of peeling consumption is already described. The above chip 1
50, for example, the above-mentioned ingot 200 manufactured by the method shown in FIG. 6 is formed into a cylindrical shape by hot forging (for example, hot swaging) or the like as shown in FIG. By forming a wire by rolling or hot drawing, and cutting the wire to a predetermined thickness in the axial direction by electric discharge machining or the like, the wire can be manufactured with a high yield.

Further, a structure as shown in FIG. 10 can be adopted. That is, in this spark plug 100,
The tip 150 is fixed to the end surface of the center electrode 3 to form the center electrode-side firing portion 31, while a plurality of ground electrodes 4 are provided, one end of which is connected to the metal shell 1 and the other end is the center electrode. It is arranged so that it is bent back to the side 3 and its front end surface faces the side surface of the center electrode side firing portion 31. In this case, the center electrode-side ignition portion 31 is configured such that the main component-based phase region 50 and the additive metal element-based phase region 51 having a flat shape are substantially perpendicular to the axial direction of the center electrode 3 (that is, the voltage application direction). (Substantially in parallel with). This makes it possible to effectively suppress the wear on the side surface of the central electrode side firing portion 31 serving as the discharge surface.

Note that the chip forming the ignition portion is
It may be formed using spherical particles produced by an atomizing method or the like. Specifically, the molten alloy is formed into spherical particles by a gas atomizing method, and particles having a predetermined size are classified by a sieve or the like, and then each spherical particle is flattened by a press or the like to form chips.

FIG. 11 shows various methods of forming the ground electrode side firing portion 32. As shown in FIG. 11A, the tip 150 made of the Rh-based noble metal alloy manufactured by the above-described method is superimposed on the side surface of the ground electrode 4,
As a result, the chip 150 forms an interface welded portion W2 corresponding to the overlapping surface thereof as shown in FIG.
It is joined to form the ground electrode side firing portion 32. The base material of the ground electrode 4 is a Ni alloy, for example, INCONEL 600 or INCONEL 601 (both are INCO UK) in order to secure high temperature strength and corrosion resistance.
(Trade name of a company) or the like. R
Since the melting point of the h-based noble metal alloy is considerably higher than that of the Ni-based heat-resistant alloy of the ground electrode base material, the ground electrode base material side softens first during resistance welding, and the tip 150 is partially embedded in the ground electrode base material. Joined.

The Ni alloy constituting the base material of the ground electrode has a considerable difference in the coefficient of thermal expansion between the Ni alloy and the Rh-based noble metal alloy. The ground electrode side firing portion 32 may cause a problem such as peeling due to the cooling and heating cycle. In this case, as shown in FIG.
Can be joined to the base material via a stress relaxation layer 161 made of a Ni-containing alloy having a lower Ni content than the ground electrode base material (for example, an Ir-40 mass% Ni alloy). The stress relaxation layer 161 is formed of the ground electrode base material and the ground electrode side ignition portion 3.
2 has an intermediate coefficient of thermal expansion between them, and by interposing this between them, excessive thermal stress is prevented from being concentrated on the interface on the joining side of the ground electrode side firing portion 32, and the firing portion is separated. And the like can be made less likely to occur.

The stress relaxation layer 161 is formed, for example, as shown in FIG.
As shown in FIG. 7, the chip 150 can be formed by stacking the chip 150 on the ground electrode 4 with the metal plate material 160 serving as the material for forming the stress relaxation layer 161 sandwiched therebetween and similarly resistance welding. In this case, the metal plate material 160 is joined to the ground electrode base material side via the interface welding portion W4 while being pressed into the ground electrode base material side, and becomes the stress relaxation layer 161. Further, the chip 150 is provided with the stress relaxation layer 1.
61 is joined via the interface welding portion W3 to form the ground electrode side firing portion 32.

Note that the ground electrode side firing portion 32 is provided in FIG.
As shown in (e), the side surface of the ground electrode 4 may be formed close to the leading edge. In FIG. 2, only the ground electrode-side firing portion 32 may be made of a Rh-based noble metal alloy, and the center electrode-side firing portion 31 may be made of an Ir-based noble metal alloy.
Further, a core material 4a made of Cu or Cu alloy for improving heat drawing may be embedded in the base material of the ground electrode 4. Thereby, lead corrosion or spark consumption of the ground electrode side ignition portion 32 can be more effectively suppressed. In addition, as shown in FIG. 1, a similar core material 3 a can be embedded in the base material of the center electrode 3.

In the configuration shown in FIG. 2, the outer diameter of the ground electrode side firing portion 32 is 0.6 to 1.6 mm, and the thickness is 0.2 to 0.1 mm.
It is desirable to set it to 8 mm. Exceeding the upper limit in any case leads to a disadvantage that the size of the ignition portion becomes unnecessarily large and waste of material easily occurs. On the other hand, when the outer diameter of the firing portion 32 is less than 0.6 mm, it becomes difficult to align the center axis of the ground electrode-side firing portion 32 with respect to the center electrode-side firing portion 31, and the central electrode side firing portion 31 is partially consumed. Etc. are likely to occur. Further, when the thickness of the ground electrode-side firing portion 32 is less than 0.2 mm, it becomes difficult to sufficiently secure the life of the ground electrode-side firing portion 32.

[0064]

(Example 1) For Rh, Re, W, Ru,
By mixing and dissolving Ir, Os and Mo at various ratios, alloys having various compositions shown in Table 1 were produced. This alloy was hot-rolled at a temperature of 700 ° C. to a thickness of 0.1 mm.
It was processed into a 5 mm plate. Subsequently, the obtained plate material was subjected to hot punching (at a temperature of 700 ° C. or higher) to obtain a disk-shaped chip having a diameter of 0.7 mm and a thickness of 0.5 mm (Nos. 1 to 23). In addition, as a comparative example, Pt-13 mass% I
r alloy (No. 21), Ir-5 mass% Pt (No. 22)
A similar chip was produced using the two types of molten alloys. Further, by a known powder sintering method, it was also fabricated chips Ir-1.7 _wt% Y 2 _{O 3} alloy (No. 23). During the rolling, the sample was heated using a predetermined furnace for each fixed pass so that the sample temperature was always maintained at 700 ° C. or higher.
The workability of each alloy was evaluated as follows.
That is, the obtained plate material is kept at 700 ° C. or higher,
In this state, the diameter is 0.7 mm and the thickness is 0.5
The process of punching out a disk-shaped chip of mm was performed continuously.
Then, "○" indicates that the punching was performed normally even after the punching was repeated 1,000 times or more, and "△" indicates that the chip was cracked or chipped or the die was damaged after about 800 times.
When the number of chips was less than 100 times, cracks, chips, or damage to the die were evaluated as "x".

Next, the chips having the compositions described above were held in the air at 1,050 ° C. for 20 hours, and the oxidation resistance was evaluated by measuring the weight loss of each test piece. Also, using these chips, the center electrode side firing portion 31 and the ground electrode side firing portion 3 of the spark plug 100 shown in FIG.
2 was formed so that the width of the spark discharge gap g was 1.1 mm, and a spark erosion resistance test was performed under the following conditions. That is, the plug is attached to the test chamber and connected to the full transistor igniter, the air pressure in the chamber is 0.4 MPa (about 4 atm), and the maximum voltage is 30 MPa.
An AC voltage having a frequency of 100 Hz was applied at kV for 250 hours, and the increase in the width of the spark discharge gap g was measured. The actual durability test of each plug was performed under the following conditions. That is, a six-cylinder gasoline engine (displacement 200
0 cc), and the cylinder was operated for 400 hours with the throttle fully opened, an engine speed of 5,000 rpm, and a polarity in which the center electrode side became negative. The fuel used was unleaded gasoline having a Pb content of less than 1 ppm. Excellent (◎) when the spark discharge gap g is less than 0.2 mm, good (○) when 0.2 to 0.5 mm, and acceptable (△) when 0.6 to 0.9 mm. 0.9
Those exceeding mm were evaluated as unacceptable (x). Table 1 shows the above results.

[0066]

[Table 1]

When an alloy falling within the scope of the claims of the present invention is used as a chip material, good results are obtained in all of oxidation resistance, spark wear resistance, workability and actual machine durability. You can see that. On the other hand, for the comparative example,
In No. 16 using a Pt-based alloy, the gap was reduced, which was considered to be caused by the sweating phenomenon of the ignition part.
In addition, in Nos. 17 and 18 using an Ir-based alloy, the oxidation and wear resistance was insufficient.

Example 2 A chip for forming a ground electrode side ignition portion was manufactured as follows. First, I
By mixing and dissolving r at various ratios of 2 to 80% by mass, Ir-Rh alloys of various compositions were produced. This alloy is hot forged, hot rolled, and hot swaged at 1200 ° C., and then hot drawn to obtain an outer diameter of 1 m.
m of alloy wire was obtained. By cutting this in the longitudinal direction, a disk-shaped chip having a diameter of 1 mm and a thickness of 0.3 mm was obtained for each composition. Further, as the tip for forming the ignition portion on the side of the center electrode, a disc-shaped tip having a diameter of 0.7 mm and a thickness of 0.3 mm was obtained in the same manner, with the alloy composition being Ir-5 mass% Pt. The tip for forming the ignition part on the ground electrode side is INCONEL600
The spark plug of the form shown in FIG. 1 and FIG. 2 is welded by laser welding to the ground electrode base material made of INCONEL600, and the tip for forming the ignition part on the center electrode side is welded to the center electrode base material made of INCONEL600 by laser welding Was manufactured.

Each spark plug is mounted on a 6-cylinder gasoline engine (displacement: 2000 cc), uses leaded gasoline containing 0.04% by mass of 4-methyl lead as fuel, and the throttle is fully opened and the engine speed is 5000 r.
At pm, operation was performed for 100 hours at a polarity where the center electrode side was negative. After the operation, the section including the axis of the ground electrode was observed with an optical microscope, and as shown in FIG.
The area of the cross-sectional corroded portion was measured from the cross-sectional size of the initial firing portion estimated from the chip size. The results are shown in FIG. That is, when the Ir content is in the range of 2 to 38% by mass, that is, the Rh content is in the range of 62 to 98% by mass, the area of the cross-section corroded portion due to the generation of the corroded portion is small, and the lead corrosion resistance is improved. Understand.

Example 3 The same spark plug as in Example 1 was used, except that a leaded gasoline containing 0.04% by mass of tetramethyl lead was used as fuel and the test time was 90 hours. Perform an actual machine durability test under the same conditions as
This was designated as lead corrosion resistance. For the ground electrode-side ignition portion, those having a cross-sectional corrosion area of less than 0.05 mm ² from the initial ignition portion cross-sectional size estimated from the chip size are excellent (◎), and 0.05 mm ² or more and less than 0.1 mm ^2. Were evaluated as good (良), those with 0.1 mm ² or more and less than 0.15 mm ² were evaluated as good (△), and those with 0.15 mm ² or more were evaluated as poor (×). Table 2 shows the above results.

[0071]

[Table 2]

In comparison with the results in Table 1, the alloy composition of the ignition portion, in which the amount of the added metal element was adjusted so that the Rh content was 62% by mass or more, was found to be resistant to spark abrasion and lead corrosion. It can be seen that both sexes are compatible.

Fourth Embodiment A spark plug having the same shape as that of the first embodiment is provided in the following three types. The ignition part on the ground electrode side is made of Rh-based noble metal, and the ignition part on the center electrode side is made of Ir-based noble metal. Produced (expressed as ground electrode side firing part composition / center electrode side firing part composition): Rh-38% by mass Ir / Ir-20% by mass Rh; Rh-38% by mass Ir / Ir-5% by mass Pt; Pure Rh (purity 99% by mass or more) / Ir-5% by mass P
t.

With respect to the three spark plugs, an actual durability test under the same conditions as in Example 1 and a lead corrosion resistance test under the same conditions as in Example 3 were performed and evaluated in the same manner. As a result, regarding lead corrosion resistance, が, ○, ◎,
Regarding the durability of the actual machine, both were ○, and good results were obtained in all cases.

[Brief description of the drawings]

FIG. 1 is a front partial sectional view showing one embodiment of a spark plug of the present invention.

FIG. 2 is an enlarged sectional view showing a main part thereof.

FIG. 3 is a schematic view of the alloy structure of the ignition portion.

FIG. 4 is an explanatory view showing an example of a method for manufacturing a chip for forming a firing portion.

FIG. 5 is an explanatory view showing a modified example of the same.

FIG. 6 is a process explanatory view showing an example of a method for producing a raw material alloy ingot for chips.

FIG. 7 is an explanatory view of a manufacturing process of an alloy plate material for manufacturing chips.

FIG. 8 is an enlarged schematic view showing an example of an alloy structure of a firing portion.

FIG. 9 is a schematic view showing a state in which the structure is flattened by rolling.

FIG. 10 is a front view showing a modified example of the spark plug of the present invention.

FIG. 11 is an explanatory view illustrating some examples of a method of forming a ground electrode-side firing portion.

FIG. 12 is an explanatory diagram of a lead corrosion evaluation method of Example 2 and a graph showing experimental results.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 metal shell 2 insulator 3 center electrode 4 ground electrode 31 firing part 32 opposing firing part g spark discharge gap

Claims (11)

[Claims] A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a ground electrode arranged to face the center electrode. An ignition portion fixed to at least one of the center electrode and the ground electrode to form a spark discharge gap, wherein the ignition portion contains Rh as a main component, and further contains Re, Ru, Ir, A spark plug mainly comprising a Rh-based noble metal alloy containing one or more selected from W, Mo and Os in a range of 3 to 38% by mass. 2. The ignition part according to claim 1, wherein the main metal element component is 6
It contains 0 to 97% by mass of Rh, and further contains one or more selected from Re, Ru, Ir, W, Mo and Os in the range of 3 to 35% by mass as an additional metal element component. 2. The spark plug according to claim 1, wherein the spark plug is mainly composed of a Rh-based noble metal alloy. 3. An amount of the additive metal element component of 5 to 15% by mass.
The spark plug according to claim 1, which is contained in the range of: 4. The additive metal element component includes Re, Mo,
The spark plug according to any one of claims 1 to 3, wherein the spark plug is mainly composed of at least one of Ir and Ru. 5. The content of Rh in the ignition part is 62 to 97.
The spark plug according to any one of claims 1 to 4, which is in mass%. 6. The ground electrode is disposed so that a side surface faces a tip end surface of the center electrode, and a ground electrode-side firing portion fixed to the ground electrode side is mainly composed of the Rh-based noble metal alloy. A spark plug according to any one of claims 1 to 5. 7. The spark plug according to claim 6, wherein a center electrode firing portion is fixed to a tip end surface of the center electrode, and the center electrode side firing portion is mainly composed of an Ir-based noble metal alloy containing Ir as a main component. . 8. A center electrode, an insulator provided outside the center electrode, a metal shell provided outside the insulator, and a side surface arranged to face a tip end surface of the center electrode. A ground electrode, a ground electrode-side ignition portion mainly composed of Rh-based noble metal mainly composed of Rh, and affixed to the tip end surface of the center electrode. And a center electrode-side ignition portion mainly composed of an Ir-based noble metal whose main component is a spark discharge gap formed between the ground electrode-side ignition portion and the center electrode-side ignition portion. Spark plug. 9. The spark plug according to claim 8, wherein said Rh-based noble metal contains 3 to 38% by mass of Ir. 10. The Rh-based noble metal has an Ir of 13 to 30.
The spark plug according to claim 8, wherein the spark plug is contained by mass%. 11. The ground electrode base material is made of a Ni-based noble metal alloy containing Ni as a main component, and the ground electrode-side ignition portion has a Ni content lower than that of the ground electrode base material.
The spark plug according to any one of claims 1 to 10, wherein the spark plug is joined to the base material via a stress relaxation layer made of a contained alloy.